You MUST do wind tunnel testing of your car to determine its drag coefficient. (Values in the order of 0.03 for a flat plate of 200 cm square to 0.003 for a low drag aerofoil shape of 200 cm square would be typical.) 137 If you cannot perform wind tunnel testing you can make an estimation of drag coefficient by taking the 0.03 drag coefficient for a flat plate of 200 cm square and calculate the drag coefficient for your car with a simple ratio calculation based on your cars frontal area compared to the 200 cm square.
This will give a worst case drag figure as it is based on a flat plate. As a help to determining your drag ratios some drag ratios of actual cars that have been tested in a wind tunnel are given below. CAUTION: The air drag coefficients listed here are not cd values or Drag Coefficient values as normally seen.
They are derived from testing of a particular car and the coefficient includes cd values as well as frontal area and air density all rolled into the one coefficient. Consequently we cannot compare the aerodynamic performance of different cars without considering their frontal area. (See section on air drag in Mathematical Simulator earlier in this document for more details) PHOTON CRUNCHER MK IV : SIMUL